1. Field of the Invention
This invention relates to a process and an apparatus for filling N2 gas into tires, and more particularly to a process and an apparatus for efficiently filling N2 gas inclusive of N2 rich gas having a high N2 concentration into tires such as passenger car tires, large-size vehicle tires (for truck and bus) and the like regardless of the kind of the tire used.
2. Description of Related Art
Since N2 gas is very durable to a temperature change, when N2 gas is filled into a tire, even if the temperature of the tire is raised during the high-speed running, severe service running or the like, the change of internal pressure in the tire is small and it is possible to prevent the lowering of the running performances and it is advantageous to improve the ride comfort. Therefore, the filling of N2 gas is adopted in special applications such as airplanes and F1 racing cars obliged to be run at a high speed.
Recently, it is generally and widely known that the filling of N2 gas into the tire develops an effect of preventing the degradation of rubber or wheel and the like. Further, the filling of N2 gas tends to be required by ordinary users with the advance of high tire performances. As a result, the filling of N2 gas is particularly carried out as a part of service in car shops, oil depots and the like. For this end, it is demanded to develop means for efficiently filling N2 gas into the tire with a relatively cheap filling cost.
As a filling system of N2 gas, there are known a method of using a commercially available cylinder filled with N2 gas for filling N2 gas into the tire, a method wherein only N2 gas is separated and purified with an industrial activated carbon while feeding compressed air through an air compressor for filling N2 gas, and a method of using a gas separation membrane wherein O2 and N2 are separated from air by utilizing a theory that permeation rates differ in accordance with a kind of gas components to thereby feed a high concentration N2 gas.
In the method of using the N2 filled cylinder, however, much labor is required in inventory control, carrying-in, carrying-out and the like of the cylinder and also it is required to ensure a setting place of the cylinder, so that this method is disadvantageous in view of the running cost. In the method using the industrial activated carbon, there is no inconvenience as mentioned above, but it is necessary that the activated carbon after the use over a certain time is subjected to a regeneration treatment for removing O2 adsorbed on the activated carbon once and hence the maintenance is inevitable. Particularly, when the filling of N2 gas is requested during the regeneration of the activated carbon, there is an inconvenience that such a request is not satisfied. And also, the method using the activated carbon has an advantage of setting the concentration of N2 gas to an arbitrary level, but when using the compressed air above 1000 kPa, a high pressure O2 gas (active gas) is gathered in a tank of a high pressure gas installation in view of its structure, so that it is disadvantageous to regulate a setting place of such an installation.
On the other hand, the method using the gas separation membrane does not cause the drawbacks as mentioned above and can relatively rapidly fill N2 gas, if necessary. And also, it is not required to use a tank gathering a high pressure O2 gas even when using a compressed air above 1000 kPa, so that the method can advantageously be used in wider fields without subjecting to the regulation for the high pressure gas installation. In this method, however, it can not be avoid that about 7% of O2 remains in a passenger car tire even when N2 gas having a concentration of 100% is filled into the tire so as to have an internal pressure of 200 kPa (even if air is merely taken out from the tire, air equal to atmospheric pressure is existent in the tire), so that it can not be said to more expect the effect by the filling of N2 gas. This is true in the above two methods. Particularly, a recommended internal pressure is higher in large size tires for truck and bus than that of the passenger car tire, so that a long time is unavoidably required in the filling of N2 gas into such a large size tire at the present. For this end, it is strongly demanded to solve these problems.
It is, therefore, an object of the invention to provide a novel process and an apparatus capable of efficiently and rapidly filling N2 gas or N2 rich gas into the tire and visually grasping concentration of N2 gas fed to the tire and concentration of N2 gas in the tire after the filling.
According to a first aspect of the invention, there is the provision of a process for filling N2 gas into a tire assembled onto a rim to hold a recommended internal pressure, characterized in that air inside the tire is discharged prior to the filling of N2 gas to render the inside of the tire into a state lower than atmospheric pressure and then N2 gas is filled into such a tire. In this case, N2 gas includes N2 rich gas having a high N2 concentration.
According to a second aspect of the invention, there is the provision of a process for filling N2 gas into a tire assembled onto a rim to hold a recommended internal pressure, characterized in that an operation for discharging out a gas filled in the tire into the atmosphere is carried out at least one times on the way of filling N2 gas.
According to a third aspect of the invention, there is the provision of a process for filing N2 gas into a tire assembled onto a rim to hold a recommended internal pressure, characterized in that air inside the tire is discharged prior to the filing of N2 gas to render the inside of the tire into a state lower than atmospheric pressure and then N2 gas is filled into such a tire, during which an operation for discharging out a gas filled in the tire into the atmosphere is carried out at least one time during the filling of N2 gas. In this case, an adjustment of controlling a flow amount of N2 gas is carried out in the filling of N2 gas.
According to a fourth aspect of the invention, there is the provision of a process for filling N2 gas into a tire assembled onto a rim to hold a recommended internal pressure, characterized in that when large size tires for use in trucks, busses and the like are used as the tire, N2 gas to be filled into the tire is fed at a pressure exceeding 1000 kPa and then adjusted to a pressure higher by at least 100 kPa than the recommended internal pressure to fill into the tire.
In a preferable embodiment of the fourth aspect, N2 gas is filled in a pressure not exceeding the feeding pressure of N2 gas in the filling into the tire.
In the filling of N2 gas into the large size tire, air inside the tire may be discharged prior to the filling of N2 gas to render the inside of the tire into a state lower than atmospheric pressure, or an operation for discharging out a gas filled in the tire into the atmosphere may be carried out at least one times on the way of filling N2 gas.
In any case, N2 gas is filled by adjusting the feeding pressure of N2 gas so as to fit into the recommended internal pressure of the tire assembled onto the rim.
According to a fifth aspect of the invention, there is the provision of an apparatus for filling N2 gas into a tire, comprising a single inlet path, at least two outlet paths and a membrane module for separating air introduced through the inlet path into O2 gas and N2 gas and feeding these gases into respective outlet paths, wherein an outlet path for feeding N2 gas in the outlet paths is connected at its top to a valve for inflating a tire assembled onto a rim under an internal pressure and a discharge path for discharging air inside the tire prior to the filling of N2 gas is provided on the way of such an outlet path.
In a preferable embodiment of the apparatus according to the invention, at least two membrane modules are arranged side by side. In another preferable embodiment of the apparatus, the air discharge path is connected to a vacuum pump and a holder storing N2 gas fed from the membrane module once is disposed in the outlet path located at an upstream side from a portion thereof connected to the air discharge path.
In the other preferable embodiment of the apparatus, a switch valve properly releasing the internal pressure of the tire is provided on the outlet path feeding N2 gas and further a flow control valve adjusting a flow amount of N2 gas is arranged on the outlet path feeding N2 gas.
In the apparatus according to the invention, a pressure adjusting means for setting pressure to a proper level in accordance with a recommended internal pressure of the tire may be arranged in the outlet path feeding N2 gas. And also, means for indicating a concentration of N2 gas may be arranged, and further means for sucking and discharging the remaining air in the tire by utilizing pressure of compressed air fed into the membrane module may be arranged. A pressure reducing valve may be used as the pressure adjusting means.
The outlet path feeding N2 gas through the membrane module is divided into two branched pathways, one of which pathways being used as a pathway feeding N2 gas at a higher pressure adaptable for a large-size tire used in vehicles such as truck, bus and the like and the other pathway being used as a pathway feeding N2 gas at a relatively low pressure adaptable for a passenger car tire or the like. In this case, the term xe2x80x9crelatively low pressurexe2x80x9d used herein means a pressure of about 200-550 kPa, and the term xe2x80x9chigher pressurexe2x80x9d means a pressure of about 550-1400 kPa.
According to the invention, when the recommended internal pressure is held in the tire assembled onto the rim by filling N2 gas, it is favorable that the concentration of N2 gas fed into the tire is continuously measured by means of a sensor during the filling of N2 gas to indicate the measured result through an indicating means at any time, or the concentration of N2 gas in the tire after the completion of the filling of N2 gas is measured to indicate the measured result through an indicating means. For this end, the apparatus according to the invention is provided with an indicating means for indicating at least one of the N2 gas concentration fed into the tire during the filling of N2 gas and the N2 gas concentration in the tire after the completion of the filling of N2 gas. In this case, an indicator indicating the measured value through the sensor for the measurement of N2 gas concentration is used as the indicating means. In the invention, the indicator is favorable to be a digital indicator.
In the outlet path feeding N2 gas may be arranged a discharge path for discharging a gas inside the tire. And also, a four-port valve used for measuring the N2 gas concentration in the tire after the filling of N2 gas may be arranged between a portion of the outlet path connected to the discharge path and the membrane module. Particularly, a valve of closed center system is favorably used as the four-port valve.
When the N2 gas separated from the compressed air is filled into the tire assembled onto the rim, air remaining in the tire may be sucked and discharged by utilizing the pressure of the compressed air prior to the filling of N2 gas to render the inside of the tire into a state lower than atmospheric pressure. In this case, the discharge of the remaining air is favorable to be carried out by using an ejector.
When a remaining air discharge means for sucking and discharging the remaining air from the inside of the tire by utilizing the pressure of the compressed air fed into the membrane module is arranged in the apparatus according to the invention, the membrane module is constructed with at least one inlet path introducing the compressed air and at least two outlet paths flowing N2 gas and O2 gas, and the remaining air discharge means is arranged between the inlet path introducing the compressed air and the outlet flowing N2 gas.
In this case, it is desirable that an ejector utilizing the pressure of the compressed air introduced into the membrane module is used as the remaining air discharge means, and a sensor measuring the N2 gas concentration and an indicating means for indicating the measured value through the sensor are arranged in the outlet path feeding N2 gas so as to visually confirm the N2 gas concentration.